The invention primarily relates to a receiver designed to detect whether persons are buried in collapsed ground. With collapsed ground is meant anything from house ruins resulting from i.e. earthquakes or explosions to avalanches. Since it is a matter of life and death to quickly excavate persons buried in the masses, all methods that quickly localize the positions to start excavating are of great interest. During for example avalanches, where large amounts of snow are swept away, it is increasingly hard to localize persons if one does not possess techniques that give a first indication of where to search. Furthermore, the inaccessibility of the collapsed ground during for example earthquakes is troublesome for the rescue crew since it is tough to force ones way through the surroundings. There is a therefore a need for a device that is both easy to use and give the rescue crew reliable indications whether persons are buried in the masses. If the device furthermore is able to indicate the locations of these persons this would also be a positive feature. A device according to the present invention provides for all these positive features.
The device according to the invention consists of at least one radar generating and radar transmitting means, a receiver device and a signal processing unit connected to said receiver device. The task of giving a first indication whether persons are buried in the masses is performed by means of transmitting a radar signal into the ground whereby the receiver is designed to receive the reflected signal. The reflected signal is subsequently analyzed in the signal processing unit to decide whether there are persons/moving objects present in the masses. The analyzing step is searching for Doppler shifts in the received signal. A Doppler shift is a phenomenon that emerges when a source is moving relative the signal transmitting device. This movement will lead to shifts in the received frequencies or wavelengths relative the transmitted ones. Since Doppler shifts are relevant when an object is moving relative the signal source, a detection of a Doppler shift in the received signal will correspond to the fact that an object in the collapsed ground is moving. The present invention is searching for those small Doppler shifts that are present when there are minor movements from the object. The minor movements could, for example, be movements pertaining to breathing whereby the chest is moving relative the signal source. Due to the very small relative movements there is needed a signal processing that is highly sensitive. The present invention comprises a signal processing unit with those features.